FIG. 16 shows a solid electrolytic capacitor of the chip type which is well known in the art (see JP-A No. 2002-246268).
The solid electrolytic capacitor 1 shown in FIG. 16 comprises a capacitor element 2 having lead frames 9, 90 attached to the bottom surface thereof. The capacitor element 2 is covered with a housing 70 of synthetic resin. The lead frames 9, 90 are bent along the housing 70. The capacitor element 2 comprises a dielectric oxide coating 21 formed on a portion of an anode body 20 which is foil of valve metal, and a cathode layer 3, a carbon layer 6 and a silver paste layer 60 successively formed over the oxide coating 21. The portion of the anode body 20 provided with the dielectric oxide coating 21 serves as a cathode 2b, and the uncoated portion of the anode body 20 not covered with the oxide coating 21 serves as an anode 2a. For the convenience of illustration, the cathode layer 3, carbon layer 6 and silver paste layer 60 are each shown in FIG. 16 as a thick layer, whereas the anode body 20 is nearly a flat sheet in actuality.
The term “valve metal” refers to a metal which forms an extremely compact dielectric oxide coating having durability when treated by electrolytic oxidation. Al (aluminum), Ta (tantalum) and Ti (titanium) are such metals.
The solid electrolytic capacitor 1 has a great height in its entirety since the lower surface of the capacitor element 2 is away from the bottom surface of the housing 70 in the direction of height. However, it is required that such capacitors be made thinner. To meet the requirement, a solid electrolytic capacitor is available which has lead frames 9, 90 each in the form of a flat plate and wherein the lower surface of a capacitor element 2 is positioned closer to the bottom surface of a housing 70 as shown in FIG. 17 (see JP-A No. 2002-25858). In the case of the capacitor 1 shown in FIG. 17, the lower surfaces of the cathode-side lead frame 90 and the anode-side lead frame 9 have approximately the same shape.
The aforementioned publication, JP-A No. 2002-246268, also discloses a capacitor element 2 which, as shown in FIG. 18, comprises a plurality of anode bodies 20, 20 adhered or welded to each other at their anode (2a) ends and having increased capacitance.
Although the solid electrolytic capacitors 1 shown in FIGS. 17 and 18 are reduced in thickness, the lead frames 9, 90 are joined to the housing 70 in intimate contact therewith with a low strength. In other words, with the capacitor 1 of FIG. 16, the housing 70 covers the upper portion of each of the lead frames 9, 90 over the upper and lower surfaces thereof and is joined to the lead frame with a great strength, whereas with the capacitors 1 shown in FIGS. 17 and 18, the housing 70 is in contact with the lead frames 9, 90 only over one surface of each lead frame and therefore over a smaller area than is the case with the capacitor of FIG. 16. Thus, the strength of the joint between the housing 70 and the lead frames 9, 90 is lower in the capacitors 1 of FIGS. 17, 18 than in the capacitor 1 of FIG. 16.
Accordingly, water is liable to ingress into the capacitor through the joint (indicated at M in FIG. 18) between the housing 70 and the lead frames 9, 90. If water reaches the capacitor element 2, the element is prone to deteriorate. The capacitor 1 therefore still remains to be improved in moisture resistant characteristics.